Monopulse interferometers are used to provide azimuth and elevation measurements of an incoming signal relative to the bore sight of the antenna. As the final angular measurement depends upon a relative phase measurement, the system for processing the incoming signal must be precisely aligned so that no phase error is introduced. The need for eliminating phase error is increased where delay lines are introduced into the system such as in a wide band steerable receiver. As the delay lines inherently carry phase change into the system, it is critical to the operation of the interferometer that any such inherent change, modifying the actual phase measurement, be calibrated so a corrected accurate phase measurement uncontaminated by the delay line phase shift or any other phase error, may be produced.